hello there !
on the gauges, if they flat line there is a couple of grounds i would like you to check first
first the ground at the steering column , second both kick panel ground points left and right (you may have to remove the kick panels to gain access to them , third the ground on the firewall in the engine compartment
all of these grounds please loosen the nut inspect for corrosion and then replace the acorn nut w/ a serrated nut and retorque and then retest !!!
there can be a chance that the instrument cluster is bad due to a loose solder joint !!! but check the grounds first !!!
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